Gas generator



Sept. 2, 1969 AcLlN ET AL 3,464,355

GAS GENERATOR Filed June 11; 1965 2 Sheets-Sheet 1 INVENTORS' JOHN J.ACL/N JOSEPH F JUN/(ER ATTORNEY Sept. 2, 1969 AL|N ET AL 3,464,355

GAS GENERATOR Filed June 11. 1965 2 Sheets-Sheet 2 [[6 ll JOHN L ZZZTS BJOSEPH F JUN/(ER WXM United States Patent 3,464,355 GAS GENERATOR JohnJ. Aclin, Herrin, and Joseph F. Junker, Marion, IlL, assignors to 01inMathieson Chemical Corporation, a corporation of Virginia Filed June 11,1965, Ser. No. 463,213 Int. Cl. F42b 5/20, 9/18, 13/46 US. Cl. 10239 9Claims ABSTRACT OF THE DISCLOSURE A gas generator including a cartridgecase and a solid propellant composition within the case and a zeolitebarrier positioned between the case and the propellant composition. Thezeolite barrier may be a rubber sheet having powdered zeolite embeddedtherein or a perforated container of granular zeolite. The rubber sheetcontaining the embedded zeolite may also contain embedded fibers whichare capable of acting as a wick for water.

This invention relates to improved power generating units, and moreparticularly to means for controlling the change in dimensions ofammonium nitrate propellants employed in gas generating units.

Gas generators in which solid gas generating charges are employed havebeen previously used as a source of power for the operation of primemovers such as internal combustion engines, motor starters, switchclosures, jet engine starters, and the like. These generators areusually formed of a cylindrical case closed at one end and open at theopposite end, the case containing an igniting means and a solid gasgenerating charge of suitable design enclosed in a weather sealpositioned between the case and charge. Recently, ammonium nitrategranules embedded in a matrix of a resinous or plastic binder such assynthetic rubber, nitrocellulose, and the like have been employed as thesolid gas generating charge in these generators. One problem that arisesis that although this type of solid propellant is dependable underrelatively mild temperature conditions, the dependability of firing ismarkedly affected when it is subjected to extreme variations intemperature conditions. Th increase in failures at extreme temperaturesis generally believed to be due to marked variations in the dimensionsof the solid propellant. For example, conventional gas generatingcharges containing ammonium nitrate have been observed to increase indimensions when subjected to temperature cycling tests which range frombetween about -65 F. to about +185 F. This increase in dimensions hasbeen thought to be associated with the changes in volume accompanyingphase transistions of the ammonium nitrate.

Ammonium nitrate has been described as changing from form V (hexagonal)to for IV (orthorhombic) at about 0 F., and from form IV to form III(orthorhombic) at about 90 F. These increases in dimensions of the gasgenerating charges have resulted in erratic combustion andoverpressurizations during operation of the units, and have alsoresulted in rupture of metal jet starter cartridge assemblies.

Temperature cycling of conventional gas generating assemblies isaccompanied by changes in the moisture content of the atmosphere withinthe assembly which may result from moisture vapor transmission throughthe generator case surrounding the propellant from chemical reactionwithin the generator, or otherwise. At elevated temperatures theatmosphere inside the generator case will contain a higher moisturecontent than it will at reduced temperatures. Ammonium nitrate is ahydroscopic material, and the solubililing of this material in condensedmoisture followed by recrystallization when the moisture evaporates mayalso constitute part of the 3,464,355 Patented Sept. 2, 1969 mechanismof propellant growth or increase in dimenslons. The recrystallization ofammonium nitrate may be a function of the breathing characteristic ofammonium nitrate. The nitrate is solubilized while the relative humiditywithin the case atmosphere is relatively high. When the relativehumidity drops, the adsorbed moisture is squeezed out or released asvapor within the case. The water may literally be squeezed from thepropellant at lower temperatures. The end result is a leaching ofammonium nitrate from the propellant surface. Small crystals and largersalt deposits are found on the grain surface and the bottom of the case.

A number of materials have been tested with temperature cycled ammoniumnitrate propellants in an attempt to reduce or eliminate the change indimensions during cycling.

Various known desiccants such as magnesium oxide, calcium oxide, calciumcarbonate and the like have been included in the gas generatingcontainer, but these have not been effective over the entire range ofextreme cycling temperatures (between 65 F. and +185 F.) to which thegas generators are subjected, particularly under test conditions. Themain disadvantage inherent in these desiccants is that although theyabsorb moisture from the atmosphere when the relative humidity is high,they release moisture into the atmosphere when the relative humidity islow.

There is a need in the industry at the present time for an effectivemeans for controlling the dimensions of solid propellants in gasgenerators subjected to extreme variations in temperature conditions,for example, through the range between 65 F. and +l F.

It is a primary object of this invention to overcome the disadvantagesinherent in conventional gas generators, particularly those in which awater soluble or hygroscopic material such as ammonium nitrate isemployed as a component of the solid propellant.

Another object of the invention is to provide an improved solidpropellant type gas generator.

It is another object of this invention to provide an improved means forcontrolling the dimensions of solid propellants containing water solubleor hygroscopic materials such as ammonium nitrate.

It is another object of the invention to provide a solid propellant gasgenerator in which the penetration of the propellant grain by water isreduced.

Still another object of the invention is to provide a thermal barrier insolid propellant gas generators which assists in shielding the generatorcase from exposure to high temperatures during firing by providing acoolant gas during combustion.

These and other objects of the invention will be apparent to one skilledin the art from the following detailed description.

FIGURE I is a plan view of a typical gas generator assembly of thisinvention.

FIGURE II is a longitudinal, cross-sectional view through lines IIII ofFIGURE I of a preferred embodiment of the gas generator of thisinvention.

It has now been discovered that the foregoing objects of the inventionare accomplished when a barrier of zeolite is positioned between theweather seal and the solid propellant charge of a gas generator.Improved gas generators of this invention not only resist penetration bywater from the atmosphere outside of the generator, but also areprovided with means to absorb moisture from the atmosphere within thegenerator case and retain this absorbed water even when subjected toextreme temperature variations. As a result, there is a markedinhibition of dimension changes in the solid propellant grain.

The barrier containing zeolite may be positioned within the gasgenerator by a variety of techniques. In one em- 3 bodiment, a sheet ofrubber having powdered zeolite embedded therein is wrapped around all ofthe outside surface, except for each end, of the solid propellant grainand the covered grain is inserted into the case of the gas generator.The discharge end of the generator is sealed with a suitable moisturebarrier.

In another embodiment, when propellants are required which generateextremely clean combustion gases, a barrier is placed between the flamesurface of the propellant and the rubber sheet to prevent combustion ofthe rubber sheet and to prevent the zeolite from being carried into thegas discharge.

In another embodiment of the invention, irregular fibers capable ofacting as a wick for water are incorporated into the rubber sheet withthe zeolite powder, thereby enhancing the contact of moisture with thezeolite particles. In still another embodiment of the invention asuitable cooling salt, such as ammonium oxalate, melamine, oxamide,ammonium formate, mixture thereof, and the like may also be dispersed inthe rubber sheet with zeolite powder in order to reduce the adversetemperature effects upon the generator case when the generator isignited.

In still another embodiment of the invention, the solid propellant grainwrapped with rubber sheet containing zeolite, with or without fibersand/or cooling salt, as the case may be, is inserted into an envelope ofa laminate of aluminum and polyethylene terephthalate. In still anotherembodiment of the invention, the barrier of zeolite is a perforatedcontainer of granular zeolite particles positioned within the generatorcase adjacent to the solid propellant grain. Such a container may beutilized as a supplement or replacement for the aforesaid rubber sheetcontaining powdered zeolite.

More in detail, any natural or synthetic zeolite having desiccatingproperties, and being capable of adsorbing and retaining water from theatmosphere in the range between about 65 F. and +18-5 F. may beemployed. The synthetic zeolites disclosed in United States Patent Nos.2,882,243 and 2,882,244, both of which are entitled Molecular SieveAdsorbents and which issued to Robert M. Milton on Apr. 14, 1959,illustrate the types of zeolite that are particularly suitable for usein the instant novel invention. The synthetic zeolites in United StatesPatent No. 2,882,243 are crystalline synthetic materials having acomposition expressed in terms of oxides as follows:

wherein M represents at least one of the materials in the groupconsisting of hydrogen, ammonium, metals in Groups I and II of thePeriodic Table, and the transition metals of the periodic table, nrepresents the valence of M, and Y may be any value up to about 6, theatoms of said material being arranged in a unit cell in such a mannerthat the X-ray powder diffraction pattern of the material is essentiallythe same as that shown in Table A of the patent.

The synthetic zeolites of United States Patent No. 2,882,244 arecrystalline synthetic materials having a composition expressed in termsof oxides as follows:

wherein M represents at least one cation having a valence of not morethan three, n represents the valence of M, and Y may be any value up toabout 8, the atoms of said material being arranged in a unit cell insuch a manner that the X-ray powder diffraction pattern of the materialis essentially the same as that shown in Table A of the patent.

The particle size of the zeolite compositions employed in thepreparation of the novel rubber sheet is generally in the range betweenabout 0.1 and about 10 microns, and preferably in the range betweenabout 0.5 and about 5 microns but slightly smaller or slightly largerparticles .4 may be employed if desired. When granular particles ofzeolite are employed for use in the perforated containers or retainingdevices, the particles may be irregular in size, for example, rods ofirregular length, up to about Mr inch, or more, having an outsidediameter between about inch and about inch and preferably between aboutinch and about /s inch diameter. However, granules having a diameterless than & inch may also be employed, providing the openings in theperforations of the retaining device are of a smaller diameter.

In the preparation of rubber sheet containing zeolite, it is preferredto employ powdered zeolite having pores with an average diameter in therange between about 3 A. and about 6 A. units, but powdered materialswith larger or smaller pore openings can be used if the material to beremoved from the atmosphere has a molecular size that is small enough topass into the pores of the zeolite.

The rubber component of the rubber sheet is any anhydrous rubber capableof maintaining strength and resilience over wide tempertaure ranges.Typical examples of suitable rubbers which may be employed for thispurpose include anhydrous coagulated or precipitated latex, (natural orsynthetic solid rubber latex) such as C-rubber (acrylicacid-polybutadiene copolymer), openchain conjugated diolefins havingfrom 4 to 8 carbon atoms exemplified by butadiene-l,3; 1,4-dimethylbutadiene-l,3; 2,3-dimethyl butadiene-l,3, and the like, or of rubberycopolymers of such diolefins and similar conjugated diolefins with eachother or with copolymerizable monomeric materials containing a singleethylenic linkage exemplified by styrene, methyl acrylate, methylmethacrylate, ethyl acrylate, ethyl methacrylate, acrylonitrile, orsimilar materials, or of rubbery polymers of chloroprene and the like,or a blend of a natural latex with a synthetic latex or a blend ofsynthetic lattices. In general, any elastomeric system capable of beingformed into a desired shape, which is not affected by water or zeoliteand which does not form products on ignition that would be deleteriousto the system may be employed.

The novel rubber sheeting of this invention is prepared, for example, byadding the rubber mixture to steam heated rolls, heated to a temperaturesufficient to soften the rubber, and the rubber is then worked betweenthe rolls until a uniform tacky sheet coats the roll and a good softbead is formed between the nip. The dry particles of zeolite are thenslowly added to the rubber on the rolls and gradually worked into thesheet. In a preferred embodiment the zeolite and rubber are preblendedin a suitable mixer prior to forming the sheets. The proportion ofzeolite added to the rubber is preferably equivalent to between about 40and about percent by weight of the rubber, but may range between about 1and about percent by weight of the rubber. Working of the mixture ofsoft rubber and zeolite is continued until a substantially uniformdispersion of the zeolite in the soft rubber is obtained. The sheet isrolled until it has a substantially uniform thickness of between about30 and about mils, but may be thinner or thicker if desired.

In a preferred embodiment of the invention, fibers capable of acting asa wick for water are admixed with the rubber and zeolite prior to orduring the formation of the rubber sheet. Suitable fibers includevegetable fibers such as cotton fibers as well as synthetic fibers suchas nylon fibers, acrylic fibers, polyester fibers, and the like.Asbestos is undesirable for this purpose since it acts as a curing agentfor the rubber in certain instances and imparts undesirable rigidity tothe resulting rubber sheet. The proportion of fibrous material added tothe rubber is equivalent to between about 0.5 and about 40, andpreferably between about 1 and about 20 percent by weight of the rubbercomposition.

In another embodiment, particles of a cooling salt such as ammoniumoxalate are added to the mixture of rubber and zeolite, with or withoutthe fibrous materials,

as the case may be, prior to or during the formation of the rubbersheet. The proportion of cooling salt added to the rubber is equivalentto between about 0.2 and about 60, and preferably between about 5 andabout 40 percent by weight of the rubber composition.

After the desired dispersion of solids in the rubber and the desiredthickness of rubber sheet are obtained, the sheet is removed from therolls, with or without cooling, and cut into the desired shapes. Theresulting rubber sheet containing the zeolite composition is capable ofabsorbing water in a proportion approaching that which can be absorbedby the original powdered zeolite alone. This novel rubber sheeting isparticularly useful as a component of solid propellant gas generators inorder to render the propellant grain impervious to penetration by water,and also to control the size of the solid propellant containing watersoluble or hygroscopic material such as ammonium nitrate.

FIGURE I is a plan view of a typical gas generator 100 of this inventionhaving a case 1 formed of a suitable material such as rubber, reinforcedplastic, wood, steel and the like. Secured to the top of case 1 is anignition assembly contact 2 having an ignition safety 3 which must beremoved prior to use.

FIGURE II is a longitudinal cross-sectional view through lines II ofFIGURE I of a novel gas generator of this invention. Case 1, havingignition assembly contact 2 and ignition safety 3 positioned at one end,is se-' cured at the opposite end by crimping or otherwise to case cover4. An igniter assembly 5 is secured to ignition assembly contact 2within case 1. Any conventional igniter assembly may be employed asigniter assembly 5, such as the type shown in United States Patent No.2,979,896 issued to Harold E. Perkins, Jr. et al. on April 18, 1961,which contains a conventional ignition composition and an electric squibhaving suitable lead wires and electrical connections for receiving anelectrical charge when gas generator 100 is inserted into the breachmechanism (all of which are not shown except for gas generator 100).

Igniter assembly 5 is positioned adjacent to an uninhibited portion ofpropellant grain 6.

When desired, an electrical charge is imparted to the igniter assembly 5of a gas generator 100 positioned in a suitable breach (not shown). Theresistance generated within the electrical squib (not shown) of theigniter assembly 5 ignites the complex ignition train which in turnignites the exposed uninhibited portion of propellant grain 6, such asthe perforation along the central longitudinal axis thereof. Secured tothe opposite end of the propellant grain 6 within the perforation alongthe central longitudinal axis is a sustainer *9 which is a very fastburning propellant system, which is more easily ignited by igniterassembly 5 than the propellant grain 6 and provides a flame forpermitting continuous combustion of the propellant grain 6 along theperforation at its central longitudinal axis. It also assists indirecting the flame and gas to the outer periphery of the propellantgrain 6 by acting as a momentary barrier to gas and flame flow throughthe perforation to the discharge end of gas generator 100. Propellantgrain 6 is secured to the interior of case 1 by means of suitable flange7. Attached to flange 7 is flame shield 8 which surrounds the exteriorcylindrical surface of propellant grain 6 and acts as a flame barrier todecrease exposure of case 1 to high temperatures.

In contact with flame shield 8 is a rubber sheet 10 having powderedzeolite dispersed therein. As indicated previously, this rubber sheetmay also have fibrous materials dispersed therein to act as a wick forwater, and particles of a cooling salt such as ammonium oxalate. Aflexible plastic envelope 11 surrounds the igniter assembly 5 and thepropellant grain 6 having flame shield 8 and rubber sheet 10 adjacentthereto. The flexible plastic envelope is preferably a laminate ofaluminum and polyethylene terephthalate, but any other substantiallywater impervious material may be employed.

Propellant grain 6 has secured at each end suitable flame restrictors 12and 13 to prevent combustion of these surfaces. Secured betweenpropellant grain 6 and sustainer 9, as well as adjacent to flamerestrictor 13, is spacer assembly 14. Positioned between case cover 4and spacer assembly 14 is zeolite packet 15 containing zeolite granules16. Secured to the top of zeolite packet 15 is zeolite packet cover 17having openings 18.

It is particularly advantageous to employ as a zeolite barrier both arubber sheet containing powdered zeolite positioned as described above,as Well as a packet of zeolite. However, if desired, either rubber sheetcontaining zeolite or the packet of zeolite may be omitted. Employing abarrier of zeolite in this manner not only inhibits the penetration ofwater into the solid propellant grain but also absorbs water that may bevolatilized or generated by chemical reaction of the propellant grainwhen it is exposed to extreme temperature conditions. Once the water isabsorbed by the zeolite, extremely high temperature and/or vacuum arenecessary to release it from the zeolite. As a result, no equilibrium isset up in the systems in which moisture is transferred between thezeolite and solid propellant grain as the temperature varies and thus,leaching of ammonium nitrate from the grain is inhibited. A gasgenerator is obtained having a solid propellant grain that is relativelystable under a wide variety of temperature conditions and substantiallyno misfires occur due to modifications of the propellant grainconfiguration.

Gas generators in which the novel desiccating system of this inventionmay be employed are also disclosed in United States Patent No.2,942,547, issued June 28, 1960 to Joseph William Rabern et al. and inUnited States Patent No. 2,979,896 issued April 18, 1961 to Harold E.Perkins, J r. et al.

The gas generating cartridge of United States Patent No. 2,942,547referred to above is a cylindrical resilient casing closed at one endand opened at the opposite end, the opened end being covered with aperforated plate. Contained within the gas generator is a solidpropellant grain comprised of granular ammonium nitrate embedded in amatrix of synthetic rubber. The grain is perforated in the center andinhibited at each end, permitting combustion of the grain at theinternal perforation as well as at the outer periphery. Combustion iseffected by energizing an electric squib which ignites a plurality ofignition charges positioned within the gas generator. A thin layer ofpolyethylene terephthalate is positioned on the outside of theperforated plane at the opened end of the gas generator and adjacent tothe inhibited end of the solid propellant grain to provide a Weatherseal for the cartridge. The novel rubber sheeting of this invention iswrapped around the outer periphery of the propellant grain prior toinserting it into the casing.

The gas generator described in US. Patent No. 2,979,896 employs apropellant grain which is inhibited on the outer periphery and on theinner perforation, but each end is uninhibited. Grains of this type mayalso be wrapped with the novel rubber sheeting of this invention. Inaddition, gas generators such as those described in either of theaforesaid patents may be provided with a container of granular zeolitepositioned in the perforation of the grain to supplement or replace therubber sheeting containing zeolite. When the zeolite barrier of thisinvention is employed within gas generators, not only is water from theoutside atmosphere prevented from penetrating the interior of the gasgenerator but also water either initially present or subsequentlypresent in the atmosphere within the gas generator is absorbed by therubber sheet, thereby inhibiting dimension changes in the solidpropellant grain. As a result greater reliability is imparted to the gasgenerator when subjected to extreme variations in temperatureconditions.

The following examples are presented to define the invention more fullywithout being limited thereby. All parts and percentages are by weightunless otherwise specified.

EXAMPLE 1 Two hundred parts of C rubber (acrylic acid-polybutadienecopolymer) were soaked in hexane to soften the rubber and then added toa Sigma blade mixer containing 400 parts of powdered zeolite and 400parts of ammonium oxalate. These ingredients were admixed for about onehour at a temperature of about 155 F. A vacuum was then applied to themixer to effect removal of hexane from the resulting mixture. Mixing wascontinued under vacuum for about 45 minutes, after which mixing wasstopped and the resulting dry granular solvent free particles wereremoved from the mixer.

The dry granular particles were added slowly to a cold two roll mill.The nip in the rolls was kept at a minimum until a continuous sheet wasformed around one roll and a head was present. The rolls were thenheated and the nip gradually adjusted to form a thin sheet of uniformthickness of about 0.070 inch. This sheet was cut into pieces having alength of about 28 inches and a width of about inches.

EXAMPLES 2 AND 3 A solid propellant containing ammonium nitrate wasprepared by admixing the following ingredients in the followingproportions:

Ingredient: Proportion, parts Ammonium nitrate 74 Acrylic acid modifiedpolybutadiene rubber 14 Guanidine nitrate 3 Sodium barbiturate 2 Carbonblack 2 Ammonium oxalate 5 When these materials were thoroughly mixed,the resultant mixture was transferred to molds where it was formed intograins having a diameter of one inch and a length of about two inches.The resulting molded grains were cured to solidify them.

One of these grains was placed in a container with two grams of thesheet containing zeolite prepared in Example 1. The results obtainedwith this grain are set forth below as Example 2.

A second grain was placed in another container with 1.6 grams ofgranular zeolite. The results obtained with this grain are set forthbelow in Example 3.

A third grain was placed in another container. The results obtained withthis grain are set forth below as Comparative Test.

The three containers were each hermetically sealed and subjected totemperature cycling conditions in which each container was maintained at65 F. for two hours and then maintained at a temperature of 160 F. fortwo hours. The containers were then subjected to a total of 30temperature cycles under these conditions. At the end of this period therespective grains were examined and the dimensions were measured. Theresults were as follows:

These tests show that the increase in dimensions of the propellantgrains were markedly reduced when subjected to severe temperatureconditions in the presence of zeolite and surface salting waseliminated.

8 EXAMPLES 4 AND 5 Percent increase in Sixty cycles Ninety cyclesDiameter Length Diameter Length 1. 0 1. 7 0. 8 l. 6 0. 9 0. 9 1. l l. 7Comparative test 5. 4 5. 7 10. 4 9. 9

These tests also show the marked effect of the zeolite upon inhibitingthe change of grain dimensions when subjected to extreme cyclingtemperature conditions.

EXAMPLE 6 A gas generator of the design shown in FIGURES I and II wasprepared having an over-all length of about 8.5 inches and an outsidediameter of about 6.46 inches. The initial outside diameter of thepropellant grain was 5.620 inches. The grain was then subjected to 30temperature cycles, in which each temperature cycle comprised storing atpercent relative humidity and sea level pressure under the followingconditions:

(A) Stored for 6 hours at 50 F.

(B) Stored for 4 hours at F. (C) Stored for 2 hours at F. (D) Stored for4 hours at 140 F.

At the end of the 30 cycles the gas generator was disassembled and theoutside diameter of the propellant grain was found to be 5.62 incheswhich was an increase of only about 0.4 percent in the diameter of thepropellant grain.

Various modifications of the invention, some of which have been referredto above, will be apparent to those skilled in the art. Therefore, we donot wish the invention to be limited except as defined in the appendedclaims. What is desired to be secured by Letters Patent 1s:

1. In a gas generating cartridge having a case with a gas discharge andsolid gas generating propellant composition within the case, an ignitionmeans adapted to ignite said solid propellant and a weather sealpositioned between said solid propellant and said case, the improvementwhich comprises a zeolite barrier positioned between said weather sealand said propellant charge, said zeolite barrier being a rubber sheethaving powdered zeolite and fibers capable of acting as a wick for waterembedded therein.

2. The gas generator of claim 1 wherein the proportion of powderedzeolite is between about 1 and about 90 percent by weight of the rubberand the proportion of the fibers are between about 0.5 and about 40percent by weight.

3. The gas generator of claim 1 wherein the proportion of fibers isbetween about 1 and about 20 percent by weight of the rubber.

4. In a gas generating cartridge having a case with a gas discharge andsolid gas generating propellant composition within the case, an ignitionmeans adapted to ignite said solid propellant and a weather sealpositioned between said solid propellant and said case, the improvementwhich comprises a zeolite barrier positioned between said weather sealand said propellant charge, said zeolite barrier being a rubber sheethaving powdered zeolite, fibers capable of acting as a wick for waterand particles of a cooling salt embedded therein.

5. The gas generator of claim 4 wherein said cooling salt is ammoniumoxalate.

6. The gas generator of claim 4 wherein the proportion of cooling saltis between about 0.2 and about 60 percent by weight of the rubber.

7. In a gas generating cartridge having a case with a gas discharge, asolid propellant composition within said case, ignition means adapted toignite said solid propellant, the improvement which comprises a zeolitebarrier positioned between said case and said propellant composition,said zeolite barrier being a rubber sheet having powdered zeolite andfibers capable of acting as a wick for water embedded therein.

8. In a gas generating cartridge having a case with a gas discharge, asolid propellant composition within said case, ignition means adapted toignite said solid propellant, the improvement which comprises a zeolitebarrier positioned between said case and said propellant composition,said zeolite barrier being a rubber sheet having powdered zeolite,fibers capable of acting as a wick for Water and particles of a coolingsalt embedded therein.

9. The gas generator of claim 8 wherein said cooling salt is ammoniumoxalate.

References Cited UNITED STATES PATENTS 2,469,350 5/1949 Lauritsen 102-49X 2,793,492 5/ 1957 Sage et al. 102-49 X 3,044,254 7/1962 Adelman252-194 X 3,204,558 9/1965 Jacobson et al. 102-38 3,245,946 4/1966OConnor 252-194 X ROBERT F. STAHL, Primary Examiner US. Cl. X.R. 60-253;260-41

